The invention relates to a harmonic drive arrangement for moving two components relative to one another.
Such a harmonic drive arrangement is known for example from U.S. Pat. No. 5,042,322 where it is used as a drive for an indexing apparatus. In this arrangement the harmonic drive must provide for sufficiently small movements to permit the accurate adjustment of angular positions of the two components relative to each other. In such applications, there are high requirements on the repeatability of the relative positions of the components and on the capability of the drive to transmit relatively high forces. Such harmonic drive arrangements may be used also in connection with work stations or in connection with robots. In the known drive arrangement, two toothed rings with different numbers of teeth are coupled by rolling members, that is specifically balls, which are always held in contact with the opposite side walls of the toothed rings.
The rolling elements, that is, the balls are supported by a pressure element or a cam plate so as to move the balls more less deeply into the space between adjacent teeth of the toothed rings such that the desired speed or distance of movement reduction of one component relative to the other is obtained. An extremely precise position adjustment of one component relative to the other is achieved in this way with the known arrangement with a reduction ratio depending on the number of teeth on the toothed rings and the difference in the number of teeth between the two toothed rings. Accurate movement control can be achieved in this manner although only in one, that is, for example, in circular direction but not in another, for example, axial direction of movement. Also, the transmission of forces is limited in as much as the balls provide for force transmitting engagement between only a part of the teeth associated with the two different components